\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
\sum_{n=0}^{\infin} \sum_{p=0}^{\infin} \frac{\partial^n}{\partial x^n} \frac{\partial^p}{\partial y^p} \frac{f(a,b)}{n!p!} (x-a)^n(y-b)^p
\end{equation*}
\end{document}
